The alkaloid camptothecin (CPT, 3), which has been isolated in 1958 by Wani and Wall from the Chinese tree Camptotheca accuminata, shows potent antiproliferative activity (M. E. Wall in Chronicles of Drug Discovery, D. Lednicer (Ed.), Am. Chem. Soc.: Washington D.C., 1993; Vol. 3, p. 327). The structure of the pentacyclic skeleton, which was also determined by Wani and Wall eight years after its discovery, contains a highly electrophilic α-hydroxy-δ-lactone ring (ring E, scheme 1), which contains the only stereocenter in form of a tertiary alcohol.

Despite its shortcomings, due to rapid hydrolysis in basic and neutral media towards the open chain carboxylate form (4, scheme 1), CPT continues to serve as an attractive and promising lead structure for the development of new anti-cancer drugs (see for example C. J. Thomas, N. J. Rahier, S. M. Hecht, Bioorg. Med. Chem. 2004, 12, 15851604).
Despite numerous attempts to develop a practical synthesis of camptothecin and derivatives thereof, up to now no really efficient synthesis is available. This is mainly because the currently known synthetic approaches suffer either from very low yields, expensive or commercially not available reagents or highly toxic reagents which may cause health hazard and environmental problems. Another major drawback of most current synthesis routes is an extensive need for column chromatographies during the reaction sequence.